This invention relates to an ink-jet printer for ejecting ink onto a sheet of paper held on a rotary drum to perform printing.
Recently, personal computers of high performance and low cost have become available, and the spread of personal computers has abruptly increased. In accordance with this trend, color printers have been also increasingly demanded. At the present stage, various types of ink-jet printers exist as color printers suitable for personal use.
Conventionally, there is a known ink-jet printer which can perform a continuous printing of 500 or more sheets, for example. This ink-jet printer has a rotary drum which rotates at a predetermined circumferential speed, and a print head for ejecting color inks onto a sheet of paper held on the peripheral surface of the rotary drum. The sheet is fed to the rotary drum from the front side of the rotary drum, and printing is performed in a state where the paper sheet is wound on the rotary drum. After printing, the paper sheet is separated from the rotary drum and discharged to the rear side of the rotary drum.
The print head includes nozzle units of, for example, yellow, cyan, magenta and black which are disposed along the peripheral surface of the rotary drum. Each of the nozzle units has ink-jet nozzles which are arranged across the paper sheet in the main scanning direction parallel to the axis of the rotary drum and which eject inks as the rotary drum rotates. Each nozzle unit is shifted in the main scanning direction at a predetermined rate, and returned to its initial position after a predetermined number of rotations for causing the nozzle unit to be moved by a distance equal to the nozzle pitch. Each nozzle unit scans the paper sheet simultaneously in the main scanning direction and the sub-scanning direction as described above, so as to eject ink onto the entire paper sheet.
When the printing speed of the above ink-jet printer is increased, positional deviation or vibration of the paper sheet may occur due to an impact produced by the sheet holding operation. Further, positional deviation of the paper sheet may also occur due to an impact produced by the sheet separating operation. In such a case, incorrect alignment is caused between print dots of color inks and this significantly deteriorates the printing quality.
In addition, the rotary drum is surrounded by a variety of process components in the ink-jet printer described above. Therefore, it is not easy to carry out jam state work of removing a jammed paper sheet and maintenance work of removing paper particles dropped from a paper sheet and attached to the rotary drum. Furthermore, the jam state work or the maintenance work cannot be started while rotation of the rotary drum continues due to inertia. If such work is done irrespective of the rotation of the rotary drum, the operator may have his or her fingers injured as a result of being caught between the drum and the process components. These problems serve as a factor of substantially reducing the printing speed.